Attachment apparatus for ceramic matrix composite materials

ABSTRACT

A first ceramic matrix composite structure having a first flange with a first aperture, and a second structure having a second flange with a second aperture are clamped together by a fastener and spring assembly. The second flange is in contact with the first flange and the apertures of the first and second flanges align with each other. A threaded fastener having a thermal expansion rate that is different than the thermal expansion rate of at least one of the first ceramic matrix composite structure and second structure extends through the aligned apertures. The fastener includes a bolt, a nut, and a spring assembly that maintains a constant clamping pressure irrespective of the thermal expansion differences between the bolt and the first ceramic matrix composite structure and second structure.

BACKGROUND

The present invention relates to the field of gas turbine engines, andmore particularly to an attachment apparatus for ceramic matrixcomposite materials in a gas turbine engine.

A typical gas turbine engine operates in an extremely harsh environmentcharacterized by very high temperatures and vibrations. A conventionalgas turbine engine includes a compressor for compressing entering air, acombustor for mixing and burning the compressed gases that emerge fromthe compressor with fuel, a turbine for expanding the hot gases togenerate thrust to propel the engine, and an exhaust nozzle for allowinghot gases to exit the engine. Thus, the exhaust nozzle must accommodateextremely hot gases exiting the engine.

Other considerations critical to engine design are avoiding air leakageand insulating certain engine components from exposure to hot gases. Onetype of a material that withstands hot temperatures is ceramic matrixcomposite (CMC) material. However, it is difficult to attach the CMCmaterial components with a metal fastening material. One obstacle toattaching CMC materials with metal is the different thermal expansionsof the materials. In general, it is difficult to attach or joindifferent materials in a gas turbine engine due to different thermalexpansion properties.

SUMMARY

An apparatus includes a first ceramic matrix structure and secondstructure that are joined together by a fastener of a differentmaterial. The first ceramic matrix structure has a first flange with afirst aperture. A second structure has a second flange with a secondaperture. The second flange is in contact with the first flange and theapertures of the first and second flanges are aligned with each other.The aligned apertures contain a threaded fastener having a thermalexpansion rate that is different than the thermal expansion rate of atleast one of the first ceramic matrix composite structure and the secondstructure. The fastener includes a spring assembly that maintains aconstant clamping pressure irrespective of the thermal expansiondifferences between the bolt and at least one of the first ceramicmatrix composite structure and the second structure.

Another embodiment is a mid-turbine frame located in a gas turbineengine, the mid-turbine frame includes a ceramic matrix compositecomponent that has a first flange with an aperture. A second componenthas a flange with an aperture that aligns with the aperture from thefirst flange. A bolt with a different thermal expansion rate than atleast one of the first ceramic matrix composite component and the secondcomponent extends through the apertures. The bolt has a head and athreaded shank. A nut is threadingly engaged onto the threaded portionof the bolt shank. A spring assembly is disposed on the bolt shankbetween the bolt head and the flanges that maintains a substantiallyconstant clamping pressure irrespective of thermal expansion differencesbetween the bolt and at least one of the first ceramic matrix compositecomponent and the second component of the mid-turbine frame.

Another embodiment is a method of assembling a mid-turbine frame for usein a gas turbine engine. The method includes positioning a first flangeof a first ceramic matrix composite component of the mid-turbine frameso that it abuts a second flange of a second component of themid-turbine frame. The first and second flanges of the first ceramicmatrix composite component and the second component are attachedtogether via a fastener with a spring assembly. The fastener istightened to cause the spring assembly to apply a force that clamps thefirst and second flanges together.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of a gas turbine engine.

FIG. 2 is a cross-sectional view of a portion of a gas turbine engine.

FIG. 3 is a cross-sectional view of a portion of a first vane adjoininga portion of a second vane.

FIG. 4 is a schematic cross-sectional view of ceramic matrix compositestructures being compressed by a fastener according to a secondembodiment.

FIG. 5 is a schematic cross-sectional view of ceramic matrix compositestructures being compressed by a fastener according to a thirdembodiment.

FIG. 6 is a schematic cross-sectional view of ceramic matrix compositestructures being compressed by a fastener according to a fourthembodiment.

FIG. 7 is a schematic cross-sectional view of ceramic matrix compositestructures being compressed by a fastener according to a fifthembodiment.

FIG. 8 is a schematic cross-sectional view of ceramic matrix compositestructures being compressed by a fastener according to a sixthembodiment.

FIG. 9 shows a schematic cross-sectional view of ceramic matrixcomposite structures being compressed by a fastener according to anseventh embodiment.

DETAILED DESCRIPTION

FIG. 1 schematically illustrates an example gas turbine engine 20 thatincludes fan section 22, compressor section 24, combustor section 26 andturbine section 28. Alternative engines might include an augmentersection (not shown) among other systems or features. Fan section 22drives air along bypass flow path B while compressor section 24 drawsair in along core flow path C where air is compressed and communicatedto combustor section 26. In combustor section 26, air is mixed with fueland ignited to generate a high pressure exhaust gas stream that expandsthrough turbine section 28 where energy is extracted and utilized todrive fan section 22 and compressor section 24.

Although the disclosed non-limiting embodiment depicts a turbofan gasturbine engine, it should be understood that the concepts describedherein are not limited to use with turbofans as the teachings may beapplied to other types of turbine engines; for example a turbine engineincluding a three-spool architecture in which three spoolsconcentrically rotate about a common axis and where a low spool enablesa low pressure turbine to drive a fan via a gearbox, an intermediatespool that enables an intermediate pressure turbine to drive a firstcompressor of the compressor section, and a high spool that enables ahigh pressure turbine to drive a high pressure compressor of thecompressor section.

The example engine 20 generally includes low speed spool 30 and highspeed spool 32 mounted for rotation about an engine central longitudinalaxis A relative to an engine static structure 36 via several bearingsystems 38. It should be understood that various bearing systems 38 atvarious locations may alternatively or additionally be provided.

Low speed spool 30 generally includes inner shaft 40 that connects fan42 and low pressure (or first) compressor section 44 to low pressure (orfirst) turbine section 46. Inner shaft 40 drives fan 42 through a speedchange device, such as geared architecture 48, to drive fan 42 at alower speed than low speed spool 30. High-speed spool 32 includes outershaft 50 that interconnects high pressure (or second) compressor section52 and high pressure (or second) turbine section 54. Inner shaft 40 andouter shaft 50 are concentric and rotate via bearing systems 38 aboutengine central longitudinal axis A.

Combustor 56 is arranged between high pressure compressor 52 and highpressure turbine 54. In one example, high pressure turbine 54 includesat least two stages to provide a double stage high pressure turbine 54.In another example, high pressure turbine 54 includes only a singlestage. As used herein, a “high pressure” compressor or turbineexperiences a higher pressure than a corresponding “low pressure”compressor or turbine.

The example low pressure turbine 46 has a pressure ratio that is greaterthan about five (5). The pressure ratio of the example low pressureturbine 46 is measured prior to an inlet of low pressure turbine 46 asrelated to the pressure measured at the outlet of low pressure turbine46 prior to an exhaust nozzle.

Mid-turbine frame 58 of engine static structure 36 is arranged generallybetween high pressure turbine 54 and low pressure turbine 46.Mid-turbine frame 58 further supports bearing systems 38 in turbinesection 28 as well as setting airflow entering low pressure turbine 46.

The core airflow C is compressed by low pressure compressor 44 then byhigh pressure compressor 52 mixed with fuel and ignited in combustor 56to produce high speed exhaust gases that are then expanded through highpressure turbine 54 and low pressure turbine 46. Mid-turbine frame 58includes vanes 60, which are in the core airflow path and function as aninlet guide vane for low pressure turbine 46. Utilizing vane 60 ofmid-turbine frame 58 as the inlet guide vane for low pressure turbine 46decreases the length of low pressure turbine 46 without increasing theaxial length of mid-turbine frame 58. Reducing or eliminating the numberof vanes in low pressure turbine 46 shortens the axial length of turbinesection 28. Thus, the compactness of gas turbine engine 20 is increasedand a higher power density may be achieved.

The disclosed gas turbine engine 20 in one example is a high-bypassgeared aircraft engine. In a further example, gas turbine engine 20includes a bypass ratio greater than about six (6), with an exampleembodiment being greater than about ten (10). The example gearedarchitecture 48 is an epicyclical gear train, such as a planetary gearsystem, star gear system or other known gear system, with a gearreduction ratio of greater than about 2.3.

In one disclosed embodiment, gas turbine engine 20 includes a bypassratio greater than about ten (10:1) and the fan diameter issignificantly larger than an outer diameter of low pressure compressor44. It should be understood, however, that the above parameters are onlyexemplary of one embodiment of a gas turbine engine including a gearedarchitecture and that the present disclosure is applicable to other gasturbine engines.

A significant amount of thrust is provided by bypass flow B due to thehigh bypass ratio. Fan section 22 of engine 20 is designed for aparticular flight condition—typically cruise at about 0.8 Mach and about35,000 feet. The flight condition of 0.8 Mach and 35,000 ft., with theengine at its best fuel consumption—also known as “bucket cruise ThrustSpecific Fuel Consumption (‘TSFC’)”—is the industry standard parameterof pound-mass (lbm) of fuel per hour being burned divided by pound-force(lbf) of thrust the engine produces at that minimum point.

“Low fan pressure ratio” is the pressure ratio across the fan bladealone, without a Fan Exit Guide Vane (“FEGV”) system. The low fanpressure ratio as disclosed herein according to one non-limitingembodiment is less than about 1.50. In another non-limiting embodimentthe low fan pressure ratio is less than about 1.45.

“Low corrected fan tip speed” is the actual fan tip speed in ft/secdivided by an industry standard temperature correction of [(Tram °R)/518.7)^(0.5)]. The “Low corrected fan tip speed”, as disclosed hereinaccording to one non-limiting embodiment, is less than about 1150ft/second.

The example gas turbine engine includes fan 42 that comprises in onenon-limiting embodiment less than about twenty-six fan blades. Inanother non-limiting embodiment, fan section 22 includes less than abouttwenty fan blades. Moreover, in one disclosed embodiment low pressureturbine 46 includes no more than about six turbine rotors schematicallyindicated at 34. In another non-limiting example embodiment low pressureturbine 46 includes about three turbine rotors. A ratio between numberof fan blades 42 and the number of low pressure turbine rotors isbetween about 3.3 and about 8.6. The example low pressure turbine 46provides the driving power to rotate fan section 22 and therefore therelationship between the number of turbine rotors 34 in low pressureturbine 46 and number of blades 42 in fan section 22 disclose an examplegas turbine engine 20 with increased power transfer efficiency.

FIG. 2 shows a cross-sectional view of a portion of the gas turbineengine 20 near the mid-turbine frame 58. As shown in FIG. 2, the highpressure (or second) turbine section 54 includes a number of rotatingblades 62 and a number of non-rotating vanes 64, and the low pressure(or first) turbine section 46 includes a number of rotating, shroudedblades 66 and a number of non-rotating vanes 68. It should be noted thatthe present invention is applicable to engines that utilize shroudedand/or unshrouded airfoils. The mid-turbine frame assembly 58 includes aduct 70, a number of non-rotating vanes 60 (only one vane 60, shown inpartial cross-section is visible in FIG. 2), and a strut 72. Thecomponents of the mid-turbine frame 58 can be formed of a metallicmaterial. The vanes 60 of the mid-turbine frame 58 are airfoil-shapedand arranged as a cascade in order to guide airflow passing through theduct 70, though only one vane 60 is visible in the cross-section of FIG.2. Each vane 60 has a leading edge 61A and an opposite trailing edge61B. The particular aerodynamic shape of the vanes 60 can vary asdesired for particular applications.

FIG. 3 is a cross-sectional view of a portion of a first vane 60Aadjoining a portion of a second vane 60B. The first vane 60A is made upof a first ceramic matrix composite structure and the second vane 60B ismade up of a second ceramic matrix composite structure. A first flange74A extends from the first vane 60A. A second flange 74B extends fromthe second vane 60B. The two flanges 74A and 74B contain apertures 76Aand 76B, respectively. A fastener 78 compresses the two flanges 74A and74B together. The fastener 78 includes a bolt 80, a nut 82, and a springassembly 84. The nut 82 contains a head 86 and a flange 88. The bolt 80contains a head 90 and a threaded shank 92. The spring assembly 84 ispositioned on the bolt 80 between the bolt head 90 and the first flange74A. The bolt 80 extends through the apertures 76A and 76B of the twoflanges 74A and 74B. The nut 82 threadingly engages the threaded boltshank 92 protruding through the two flanges 74A and 74B and compressesthe two flanges 74A and 74B against the force of the spring assembly 84.Functionally, the spring assembly 84 maintains a uniform pressure on thetwo flanges 74A and 74B. The spring assembly 84 is used to maintain apre-load force on the two flanges 74A and 74B by allowing standardtorquing of the bolt 80 and nut 82. Standard torquing on the bolt 80 andnut 82 prevents over-torquing of the bolt 80 and nut 82 which can causedamage to the two flanges 74A and 74B.

Spring assembly 84 can be made up of Belleville washers or other typesof springs. Spring assembly 84 can consist of one or multiple Bellevillewashers. The Belleville washers can be in series or parallel. The springrate is tailored by the number and configuration of the Bellevillewashers.

According to the present embodiment of FIG. 3, the spring assembly 84includes six Belleville washers 94. The two Belleville washers 96located nearest the bolt head 90 are facing concave away from the bolthead 90 and concave towards the two flanges 74A and 74B. The twoBelleville washers 98 located nearest the two flanges 74A and 74B arefacing concave away from the bolt head 90 and concave towards the twoflanges 74A and 74B. The two Belleville washers 100, located in betweenthe Belleville washers 96 located nearest the bolt head 90 and theBelleville washers 98 located nearest the two flanges 74A and 74B, areoriented to face concave towards the bolt head 90 and concave away fromthe two flanges 74A and 74B. Although this embodiment shows sixBelleville washers 94, other combinations may include more or fewerBelleville washers 94 oriented in the same direction as the Bellevillewashers 94 shown in FIG. 3.

The pre-load force on the two flanges 74A and 74B may be adjusted byvarying the size, quantity, and configuration of Belleville washers 94;the length of the bolt 80; and the torque applied to fastener 78. Thesize, quantity, and configuration of Belleville washers 94 are selectedto provide the necessary clamping force required throughout engineoperation, while remaining in a linear spring resiliency range. The loadprovided by Belleville washers 94 is therefore consistent for alloperating conditions, regardless of thermal growth in fastener 78 andbolt stack members.

FIG. 4 shows a schematic cross-sectional view of ceramic matrixcomposite structures being compressed by a fastener 78 according to asecond embodiment. According to this embodiment, the spring assembly 84includes two Belleville washers 94. The Belleville washer 102 locatednearest the bolt head 90 is facing concave away from the bolt head 90and concave towards the two flanges 74A and 74B. The Belleville washer104 located nearest the two flanges 74A and 74B is facing concavetowards the bolt head 90 and concave away from the two flanges 74A and74B. Although this embodiment shows two Belleville washers 94, othercombinations may include additional Belleville washers oriented in thesame direction as the Belleville washers 94 shown in FIG. 4.

FIG. 5 shows a schematic cross-sectional view of ceramic matrixcomposite structures being compressed by a fastener 78 according to athird embodiment. According to this embodiment, the spring assembly 84includes three Belleville washers 94. The Belleville washers 94 arefacing concave away from the bolt head 90 and concave towards the twoflanges 74A and 74B. Although this embodiment shows three Bellevillewashers 94, other combinations may include more or fewer Bellevillewashers 94 oriented in the same direction as the Belleville washers 94shown in FIG. 5.

FIG. 6 shows a schematic cross-sectional view of ceramic matrixcomposite structures being compressed by a fastener 78 according to afourth embodiment. According to this embodiment, a spring assembly 84Bis positioned on the bolt 80 between the nut 82 and the second flange74B. The spring assembly 84B includes six Belleville washers 94B. Thetwo Belleville washers 106 located nearest the nut 82 are facing concaveaway from the nut 82 and concave towards the two flanges 74A and 74B.The two Belleville washers 108 located nearest the two flanges 74A and74B are facing concave away from the nut 82 and concave towards the twoflanges 74A and 74B. The two Belleville washers 110, located in betweenthe Belleville washers 106 located nearest the nut 82 and the Bellevillewashers 108 located nearest the two flanges 74A and 74B, are oriented toface concave towards the nut 82 and concave away from the two flanges74A and 74B. Although this embodiment shows six Belleville washers 94B,other combinations may include more or fewer Belleville washers 94Boriented in the same direction as the Belleville washers 94B shown inFIG. 6.

The fastener of FIG. 6 also includes a spring assembly 84A positioned onthe bolt 80 between the bolt head 90 and the first flange 74A, andincludes three Belleville washers 94A. The Belleville washers 94A arefacing concave away from the bolt head 90 and concave towards the twoflanges 74A and 74B. Although this embodiment shows the spring assembly84A consisting of three Belleville washers 94A, other combinations mayinclude more or fewer Belleville washers 94A such as described in FIG.3-5.

FIG. 7 shows a schematic cross-sectional view of ceramic matrixcomposite structures being compressed by a fastener 78 according to afifth embodiment. According to this embodiment, a spring assembly 84B ispositioned on the bolt 80 between the nut 82 and the second flange 74B.According to the present embodiment, the spring assembly 84B includestwo Belleville washers 94B. The Belleville washer 112 located nearestthe nut 82 is facing concave away from the nut 82 and concave towardsthe two flanges 74A and 74B. The Belleville washer 114 located nearestthe two flanges 74A and 74B is facing concave towards the nut 82 andconcave away from the two flanges 74A and 74B. Although this embodimentshows two Belleville washers 94B, other combinations may includeadditional Belleville washers 94B similarly situated to the twoBelleville washers 94B shown in FIG. 7.

The fastener of FIG. 7 also includes a spring assembly 84A positioned onthe bolt 80 between the bolt head 90 and the first flange 74A, andincludes three Belleville washers 94A. The Belleville washers 94A arefacing concave away from the bolt head 90 and concave towards the twoflanges 74A and 74B. Although this embodiment shows the spring assembly84A consisting of three Belleville washers 94A, other combinations mayinclude more or fewer Belleville washers 94A such as described in FIG.3-5.

FIG. 8 shows a schematic cross-sectional view of ceramic matrixcomposite structures being compressed by a fastener 78 according to asixth embodiment. According to this embodiment, a spring assembly 84B ispositioned on the bolt 80 between the nut 82 and the second flange 74B.According to this embodiment, the spring assembly 84B includes threeBelleville washers 94B. The Belleville washers 94B are facing concaveaway from nut 82 and concave towards the two flanges 74A and 74B.Although this embodiment shows three Belleville washers 94B, othercombinations may include more or fewer Belleville washers 94B orientedin the same direction as the Belleville washers 94B shown in FIG. 8.

The fastener of FIG. 8 also includes a spring assembly 84A positioned onthe bolt 80 between the bolt head 90 and the first flange 74A, andincludes three Belleville washers 94A. The Belleville washers 94A arefacing concave away from the bolt head 90 and concave towards the twoflanges 74A and 74B. Although this embodiment shows the spring assembly84A consisting of three Belleville washers 94A, other combinations mayinclude more or fewer Belleville washers 94A such as described in FIG.3-5.

FIG. 9 shows a schematic cross-sectional view of ceramic matrixcomposite structures being compressed by a fastener 78 according to anseventh embodiment. According to this embodiment, a flat washer 116 ispositioned on the bolt 80 between the nut 82 and a spring assembly 84B.The spring assembly 84B includes four Belleville washers 94B. The twoBelleville washers 106 located nearest the flat washer 116 are facingconcave away from the flat washer 116 and concave towards the twoflanges 74A and 74B. The two Belleville washers 108 located nearest thetwo flanges 74A and 74B are facing concave away from the flat washer 116and concave towards the two flanges 74A and 74B. Although thisembodiment shows one flat washer 116, other combinations may includemore flat washers 116 positioned in the same or different locations asthe flat washer 116 shown in FIG. 9.

Although the embodiments have been discussed as having both structures(eg. vanes 60A and 60B) of ceramic matrix composite material, thefastener with a spring assembly is also useful where only one of the twostructures being joined is a ceramic matrix composite structure.

While the invention has been described with reference to an exemplaryembodiment(s), it will be understood by those skilled in the art thatvarious changes may be made and equivalents may be substituted forelements thereof without departing from the scope of the invention. Inaddition, many modifications may be made to adapt a particular situationor material to the teachings of the invention without departing from theessential scope thereof. Therefore, it is intended that the inventionnot be limited to the particular embodiment(s) disclosed, but that theinvention will include all embodiments falling within the scope of theappended claims.

DISCUSSION OF POSSIBLE EMBODIMENTS

The following are non-exclusive descriptions of possible embodiments ofthe present invention.

An apparatus comprising can include a first ceramic matrix compositestructure, having a first flange with a first aperture. The apparatuscan have a second structure, having a second flange with a secondaperture. The second flange can be in contact with the first flange. Thesecond aperture can be aligned with the first aperture. The fastener canhave a portion extending through the first aperture of the first flangeand the second aperture of the second flange. The fastener can have athermal expansion rate different than a thermal expansion rate of atleast one of the first ceramic matrix composite structure and the secondstructure. The fastener can include a spring assembly that maintains aclamping pressure irrespective of thermal expansion differences betweenthe fastener and at least one of the first ceramic matrix compositestructure and the second structure.

The apparatus of the preceding paragraph can optionally include,additionally and/or alternatively any, one or more of the followingfeatures, configurations and/or additional components:

the fastener can include a bolt and a nut;

the bolt can include a bolt head at a first end of the bolt and athreaded shank at a second end opposite the bolt head;

the nut can include a nut body and a flange at one end of the nut bodywith the flange extending outward from an outer surface of the nut;

the spring assembly can be located on the bolt between at least one ofthe bolt head and the nut and the first flange of the first ceramicmatrix composite structure and the second flange of the secondstructure;

the spring assembly can include at least one Belleville washer;

the spring assembly can include a plurality of Belleville washers;

at least one of the plurality of Belleville washers can face concaveaway from and adjacent to the bolt head;

the plurality of Belleville washers can include Belleville washersfacing in opposite directions; and/or

the second structure can include a ceramic matrix composite material.

A mid-turbine frame located in a gas turbine engine can include a firstceramic matrix composite component of the mid-turbine frame. The firstcomponent can have a first flange with a first aperture. The secondcomponent can have a second flange with a second aperture. The secondflange can be in contact with the first flange with the second aperturealigned with the first aperture. The bolt can extend through the firstaperture and the second aperture. The bolt can have a thermal expansionrate different than a thermal expansion rate of at least one of thefirst ceramic matrix composite component of the mid-turbine frame andthe second component of the mid-turbine frame. The bolt can have a headand a bolt shank having a threaded portion. The nut can be threadinglyengaged onto the threaded portion of the bolt shank. The spring assemblycan be disposed on the bolt shank between at least one of the bolt headand the nut and the first flange and the second flange that maintains aclamping pressure irrespective of thermal expansion differences betweenthe fastener and at least one of the first ceramic matrix compositecomponent of the mid-turbine frame and the second component of themid-turbine frame.

The apparatus of the preceding paragraph can optionally include,additionally and/or alternatively any, one or more of the followingfeatures, configurations and/or additional components:

the spring assembly can include at least one Belleville washer;

the spring assembly can include a plurality of Belleville washers;

at least one of the plurality of Belleville washers can face concaveaway from and adjacent to the bolt head;

the plurality of Belleville washers can include Belleville washersfacing in opposite directions; and/or

the second component can include a ceramic matrix composite material.

A method of assembling a mid-turbine frame for use in a gas turbineengine can include positioning a first flange of a first ceramic matrixcomposite component of the mid-turbine frame abutting a second flange ofa second component of the mid-turbine frame. The first flange of thefirst ceramic matrix composite component of the mid-turbine frame can beattached to the second flange of the second component of the mid-turbineframe via a fastener having a spring assembly thereon. The fastener tocan be tightened to cause the spring assembly to apply a force thatclamps the first and second flanges together.

The method of assembling a mid-turbine frame for use in a gas turbineengine of the preceding paragraph can optionally include, additionallyand/or alternatively any, one or more of the following features,configurations and/or additional steps:

the fastener can further include a bolt and a nut;

the bolt can include a bolt head at a first end of the bolt and athreaded shank at a second end opposite the bolt head;

the first flange of the first ceramic matrix composite component of themid-turbine frame can be compressed against the second flange of thesecond component of the mid-turbine frame by threadingly engaging thenut onto the threaded bolt shank;

the spring assembly can be disposed onto the bolt between at least oneof the bolt head and the nut and the first flange of the first ceramicmatrix composite component of the mid-turbine frame and the secondflange of the second component of the mid-turbine frame;

the spring assembly can include at least one Belleville washer;

the spring assembly can include a plurality of Belleville washers;

at least one of the plurality of Belleville washers can face concaveaway from and adjacent to the bolt head;

the plurality of Belleville washers can include Belleville washersfacing in opposite directions; and/or

the second structure can include a ceramic matrix composite material.

1. An apparatus comprising: a first ceramic matrix composite structure,having a first flange with a first aperture; a second structure, havinga second flange with a second aperture, the second flange being incontact with the first flange with the second aperture aligned with thefirst aperture; and a fastener having a portion extending through thefirst aperture of the first flange and the second aperture of the secondflange, the fastener having a thermal expansion rate different than athermal expansion rate of at least one of the first ceramic matrixcomposite structure and the second structure; the fastener including aspring assembly that maintains a clamping pressure irrespective ofthermal expansion differences between the fastener and at least one ofthe first ceramic matrix composite structure and the second structure.2. The apparatus of claim 1, wherein the fastener further includes abolt and a nut.
 3. The apparatus of claim 2, wherein the bolt comprisesa bolt head at a first end of the bolt and a threaded shank at a secondend opposite the bolt head.
 4. The apparatus of claim 2, wherein the nutcomprises a nut body and a flange at one end of the nut body with theflange extending outward from an outer surface of the nut.
 5. Theapparatus of claim 1, wherein the spring assembly is located on the boltbetween at least one of the bolt head and the nut and the first flangeof the first ceramic matrix composite structure and the second flange ofthe second structure.
 6. The apparatus of claim 1, wherein the springassembly comprises at least one Belleville washer.
 7. The apparatus ofclaim 6, wherein the spring assembly comprises a plurality of Bellevillewashers.
 8. The apparatus of claim 7, wherein at least one of theplurality of Belleville washers faces concave away from and adjacent tothe bolt head.
 9. The apparatus of claim 7, wherein the plurality ofBelleville washers include Belleville washers facing in oppositedirections.
 10. The apparatus of claim 1, wherein the second structurecomprises a ceramic matrix composite material.
 11. A mid-turbine framelocated in a gas turbine engine, the mid-turbine frame comprising: afirst ceramic matrix composite component of the mid-turbine frame, thefirst component having a first flange with a first aperture; a secondcomponent of the mid-turbine frame, the second component having a secondflange with a second aperture, the second flange being in contact withthe first flange with the second aperture aligned with the firstaperture; a bolt extending through the first aperture and the secondaperture, the bolt having a thermal expansion rate different than athermal expansion rate of at least one of the first ceramic matrixcomposite component of the mid-turbine frame and the second component ofthe mid-turbine frame, the bolt having a head and a bolt shank having athreaded portion; a nut threadingly engaged onto the threaded portion ofthe bolt shank; and a spring assembly disposed on the bolt shank betweenat least one of the bolt head and the nut and the first flange and thesecond flange that maintains a clamping pressure irrespective of thermalexpansion differences between the fastener and at least one of the firstceramic matrix composite component of the mid-turbine frame and thesecond component of the mid-turbine frame.
 12. The mid-turbine frame ofclaim 11, wherein the spring assembly comprises at least one Bellevillewasher.
 13. The mid-turbine frame of claim 12, wherein the springassembly comprises a plurality of Belleville washers.
 14. Themid-turbine frame of claim 13, wherein at least one of the plurality ofBelleville washers faces concave away from and adjacent to the bolthead.
 15. The mid-turbine frame of claim 14, wherein the plurality ofBelleville washers include Belleville washers facing in oppositedirections.
 16. The mid-turbine frame of claim 11, wherein the secondcomponent comprises a ceramic matrix composite material.
 17. A method ofassembling a mid-turbine frame for use in a gas turbine engine, themethod comprising: positioning a first flange of a first ceramic matrixcomposite component of the mid-turbine frame abutting a second flange ofa second component of the mid-turbine frame; attaching the first flangeof the first ceramic matrix composite component of the mid-turbine frameto the second flange of the second component of the mid-turbine framevia a fastener having a spring assembly thereon; and tightening thefastener to cause the spring assembly to apply a force that clamps thefirst and second flanges together.
 18. The method of claim 17, whereinthe fastener further includes a bolt and a nut.
 19. The method of claim18, wherein the bolt comprises a bolt head at a first end of the boltand a threaded shank at a second end opposite the bolt head.
 20. Themethod of claim 19, further comprising compressing the first flange ofthe first ceramic matrix composite component of the mid-turbine frameagainst the second flange of the second component of the mid-turbineframe by threadingly engaging the nut onto the threaded bolt shank. 21.The method of claim 17, further comprising disposing the spring assemblyonto the bolt between at least one of the bolt head and the nut and thefirst flange of the first ceramic matrix composite component of themid-turbine frame and the second flange of the second component of themid-turbine frame.
 22. The method of claim 17, wherein the springassembly comprises at least one Belleville washer.
 23. The method ofclaim 22, wherein the spring assembly comprises a plurality ofBelleville washers.
 24. The method of claim 23, wherein at least one ofthe plurality of Belleville washers faces concave away from and adjacentto the bolt head.
 25. The method of claim 24, wherein the plurality ofBelleville washers include Belleville washers facing in oppositedirections.
 26. The method of claim 17, wherein the second componentcomprises a ceramic matrix composite material.